1. Field of the Invention
The present invention relates to a variable optical attenuator and a ranging apparatus using the variable optical attenuator.
2. Description of the Related Art
A ranging apparatus for measuring a distance by irradiating light to a subject and receiving the light reflected from the subject has been known (Japanese Patent Laid-Open Publication Number 2001-162517).
The ranging apparatus has a variable optical attenuator having a density filter which adjusts a light power of an internal reference-light path and an external measurement-light path. The density filter has a density gradient in a rotational direction, and a density, that is to say, a light power is switched depending on the density gradient by rotating the density filter at a desirable angle by a motor so that a desirable light power can be output.
However, since the above-mentioned density filter having the density gradient is required to have a large size and to be rotated by the motor, there is a problem in that it is difficult to rapidly switch the density.